Sound reproducer



y 1934- H. R. PARSHALL 1,959,005

S OUND 'REPRODUC ER Original Filed March 10, 1930 2 Sheets-Sheet l m m mInuen or Herr 5r H.P5r5hal7 W W H27? May 15, 1934. H. R. PARSHALL1,959,005

SOUND REPRODUCER Original Filed March 19, 1930 2 Sheets-Sheet, 2

iIW///////////////// Inusn UI'- Harry H.FarshaZZ Patented May 15, 1934UNITED STATES PATENT OFFICE Application March 10, 1930, Serial No.434,484 Renewed September 10, 1931 9 Claims.

My invention relatesin general to a sound reproducer, and morespecifically to an improved reproducer or loud speaker employing theprinciple of magnetostriction and so designed as to utilize thismagnetic action to the greatest extent.

The principle of magnetostriction which consists in the elongation andshortening of a metallic bar when subjected to variations of magneticflux passing therethrough has been known for a great many years sinceits discovery by Professor Page, but it has not been utilized to a greatextent.

In the loud speaker of my invention I have utilized this principle andhave so designed the moving part of the speaker that I am able to obtaingreat volume and still retain clearness and quality. This ispossible dueto the fact that the moving body of the speaker is very light in weightand has'no inertia or audible harmonics of its own to interfere with itsoperation by alternating cur-, rents over a great range of frequency. Ithas been found that nickel shrinks or short ens with increases inmagnetic flux, and that iron, cobalt, or like metals expand or lengthenas the magnetic flux therethrough increases. Any of these metals may beused with success in a speaker of my design. At present it seems that arod of nickel alloy adapts itself best to such a speaker and its use iscontemplated, however it will be understood that any such metal rod maybe used. Also in the adaptation of my invention illustrated I have showna certain type of speaker using a cone with its edges secured but itshould be understood that the principle of my invention may be as wellutilized with any type of device for producing sound; a free edge cone,double cone, ordinary diaphragm, or any other practical types and suchdetails of mounting, etc., are only shown diagrammatically for thepurpose of illustration. The variations in the length of a shortmetallic rod due to magnetic variations are small and vary omewhat inaccordance with the molecular structure of the rod,a'nd also to thedegree of magnetization of the rod;

In the speaker herein described I utilize a rod of nickel alloy or thelike which is flattened at its center point to a thin structure andhaving its two ends bent to form an angle of approximately five degrees.The two ends of the rod are firmly secured and the elongations andcontractions, therefore, cause the rod to bend at its center point. Thusthe 'elongations and contractions are translated into a sidewisemovement of the center of the rod which is secured to the diaphragm orcone and this sidewise movement is approximately six times greater thanthe elongations in the rod.

In addition I provide a permanent magnet, of such strength as to bringthe metal of the rod to its point of greatest sensitivity at which pointgiven variations of magnetic flux produce the greatest variations inlength of the rod.

Further details of my improved speaker will be apparent from thefollowing detailed description, reference being had to the accompanyingdrawings in which:

Fig. 1 is a rear view of a cone speaker embodying the features of theinvention.

Fig. 2 is a top view of the speaker of Fig. l with certain parts shownin cross-section to clarify the description.

Fig. 3 is a sectional view of the center point of the rod 19 of Fig. 1to more clearly show the method of fastening the same.

Fig. 4 is a rear view of a modified form of speaker also embodying myinvention.

Fig. 5 is a side view of the speaker of Fig. 4 with certain parts shownin section. r

Fig. 6 is another modification showing another adaptation of theinvention.

Fig. 7 is a side view of the speaker in Fig. 6 with certain parts shownin section.

Referring now to Figs. 1 and 2, I have shown a well-known type of conespeaker having an operating unit constructed in accordance with myinvention. At 1 is a base to which is attached the usual standard orupright 2 by means of screws. To the upright 2 is secured,- by bolts,the usual spider or cone support 3. The cone 4 is secured to a strip ofchamois 6 clamped between structure 5 and spider 3 by a series of boltsand nuts. Mounted on theupright back of the apex of the cone 4 is astrong permanent magnet 7 of hardened steel with its ends bent backwardand having a large 'hole through each end of the two backward extendingends. Mounted on the ends of magnet Y? are a'pair of coils 8 and 9 eachwound with alike number of turns of copper wire. Coils 8 and 9 are woundon a tube of fibre or like insulating material such as shown at 10 inFig. 2, or on a nonmagnetic metallic tube properly slotted to preventany inductive lag or'slow-acting eifect. A pair of metallic sleeves 11and 12 are secured over each end of tube 10 and the spool heads aresecured to sleeves 11 and 12 in any manner such as swedging. Over theoutside of sleeve 11 is a soft iron collar 13 held in place over sleeve11 by screw 14. One end of sleeve 13 is threaded on the inside toreceive a hollow stud 15, also of soft iron. The stud 15 has a nut onthe outside and is screwed into sleeve 13 to securely hold the coilassembly against magnet 7 and to complete the magnetic circuit to rod19. The other end of coil 9 is held in a bracket 16 mounted on the screw17 which bracket has a hole slightly smaller than sleeve 12 and isnotched or slotted at 18so that sleeve 12 may be inserted therein andheld without play. Although, I have shown only the construction of coil9 and its mounting in detail, the coil 8 is constructed and held inexactly the same manner.

Before mounting coils 8 and 9 on the ends of magnet 7, the rod 19 isinserted into the hollow cores of coils 8 and 9. Inside of the studs 15and 20 is a hole of small diameter at one end, shown in Fig. 2, whichprovides a bearing for rod 19. The rod 19 is secured'by set screws 24and 25 which hold the rod tightly in the studs as shown. At its centerpoint rod 19 is flattened out to a strip of thin metal as shown indetail in Fig. 3. In the center a hole is drilled and in this hole asmall brass bushing 26 is inserted and either riveted, as shown, or heldby a lock nut. The pin 27 is screwed in a threaded hole through bushing26; and held in place by nut 28. At each end or near each end rod 19 isalso flattened out as shown at 23, these flattened parts act as hingesand if desired might be thin springs welded to the rod permitting freevibration thereof.

It will be noticed that the ends of magnet 7 are bent at an angleslightly less than 90, and that the holes in brackets -16 and 29 arefarther from magnet 17- so that coils 8 and 9 are mounted at an angle ofapproximately 5 in accordance with the bend in rod 19. Thus when setscrews 24 and 25 are tightened against the ends of rod 19 the rod iscentralized and the connection with pin 27, which connects with the cone4 in the usual manner, is held at a center point and rod 19 is'held inthe center of the hollow sleeves inside magnets 8 and 9. Rod 19 is thusmagnetized by magnet 7 through the soft iron parts to maintain itsmolecules in a state where, changes in the flux therein cause greatestchanges in the length of the rod. The coils of magnets 8 and 9 areconnected in series and to the output of a radio-set or other audiofrequency amplifying system from which alternating current from theoutput is passed through the coils. This alternating current alternatelyincreases and decreases the magnetic flux passing through rod 19 and therod increases and decreases in length in accordance with the strength ofthe changes in flux. The ends of the rod being securely held, suchincreases and decreases in length cause the center point of rod 19 tomovelaterally, bending at the points adjacent to bushing 26 and at 23where the metal is thin. This lateral movement causes endwise movementof ,pin 27 and thereby vibrates cone 4 in accordance with the variationsof the alternating current output from the radio receiving set. It willbe understood that the thin part of rod 19 acts asa hinge and that theconstruction shown is for illustrative purposes only. Other similarconstructions may be utilized, such as a. hinged or pivoted connectionof the rod 19 to pin 2'7.

Referring to Figs. 4 and. 5, I have shown a modified form of myinvention showing a pair of coils 30 and 31 similar to 'coils 8 and 9of-Figs. 1 and 2 and'having a rod 32 similar to rod 19. In this modifcation the main difference is a substitute for permanent magnet 7,. Inthis embodiment I providea pair of bar magnets 33 and 34 secured by apair of soft iron cross pieces 35 and 36 in the sides of which themagnets are held by means of screws as shown. The magnets andcross-pieces are held against the upright 37 by brackets, either weldedto the magnets as shown.

or attached thereto by screws. I have not endeavored to show-all thedetails of the entire speaker as details of known construction maybeadded and are immaterial to the invention. The main distinction betweenthis modification and Figs. 1 and 2 is that the two bar-magnets 33 and34 permit coils 30 and 31 to be bent at a similar angle to coils 8 and 9but toward the cone instead of away from it. Thus the pin 39 may beshorter than was pin 27 of Figs. 1 and 2, and the apex of'the angle ofrod 32 nearer'to the apex of the the. cone 38. If desired the pin 39 maybe eliminated by fastening the cone directly to the center of rod 32.Also this construction permits the use of magnets of greater strengthand mechanical rigidity. It will be understood that rod 32 and coils 30and 31 may be secured and mounted in the same manner-as the structureof. Figs. 1 and 2 or by any other equivalent mechanical means.

Referring now to Figs. 6 and 7, I have shown another modification of myinvention consistingof a sort of umbrella. construction comprising threemagnets 40, 41, and 42, each constructed in a manner similar to magnets8 and 9 and Figs.

1 and 2, and each having a rod similar to rod 19 secured therein. Inthis case the three rods through coils 40, 41 and 42 are secured attheir outer ends as was rod 19 and all are welded or otherwise securelyfastened at the inner ends to a three-pointed spider construction 43 ofthin metal. The coils 40,41, and 42 are mounted on an angle and each hasa permanent magnet at 44, 45, and 46 to magnetize the rods, the coilsare preferably connected in series and in such manner that similarmagnet poles are in the central point and variations in the currentthrough the coils will cause corresponding simultaneousvariations in thethree rods which in turn will cause the endwise movement of pin 47' tovibrate cone 48.

This construction, it will be seen, as well as that of the modificationshown in Figs. 4 and 5, operates on the same principle as that shown inFigs. 1 and 2. The magnetization of the rods by permanent magnets, suchas shown. brings the molecular structure of the nickel alloy rods tosuch a condition that slight changes in the flux produced by the coilsproduces the maximum change in the length of said rods. The angularposition of the rods and the securing of the ends in the manner showncauses the maximum vibration of the cone. It will be seen also that thevibrating unit of the speaker is very light and is free to followchanges in magnetic flux without introducing any auxiliary vibrations ofits own due to mechanical inertia. Although in Figs. 6 and 7, I haveshown the coils and rods at a somewhatgreater angle than in the otherfiguresit should be understood that this angle may as well be the sameas thatused in the other form with rods 19 and 32. Furthermore, it willbe understood that in all of the forms of the invention shown I may useelectromagnets in place of the permanent magnets shown to magnetize therods.

These electromagnetsmay be energized by direct current from a separatesource or by the plate current from the radio set or similar audiofrequency amplifying system if desired.

If electromagnets are Tised, then elements of soft iron or the like willbe used in place of the permanent magnets to provide ,the return pathfor the magnetic flux and also to maintain structural rigidity. In.eithe'r case, magnetostrictive changes in the iron or in the elementsabove mentioned isof course opposite to the changes in 15o the rods ofnickel iron alloy. Itis therefore apparent that the contrary action ofthe iron supporting frame including the permanent magnets and the coresof the electromagnets will be cumulative in effect upon the diaphragm.

From the above description it will be seen that a novel system forproviding mechanical move ments has been devised in which a completelyclosed magnetic circuit is utilized, this closed magnetic circuit inFig. 2, for instance, includes the permanent magnet '7, elements 15, androds 19. It will be seen that whether electro or permanent magnets areused the magnetic circuit may be completely closed as described. Themechanical movement will still be attained even, though a break orbreaks in the magnetic circuit is used in the mechanical construction.

It will, therefore, be seen that I have provided a very efficient typeof loud speaker which is so designed as to utilize the magnetostrictiveproperties of metal to the greatest degree. The design causing changesin length of a rod to be amplified to give sufiicient power withoutdistortion. Having fully described the invention and ascertained thefeatures and aspects of my invention, what I consider to be new anddesire to have protected by Letters Patent will be pointed out in theappended claims.

What is claimed is:

1. In a sound reproducer, a metallic member bent at an intermediatepoint in the form of an obtuse angle and secured at both ends, adiaphragm secured to said intermediate point of said member, helicesaround said member connected in a source of alternating current, thecurrent flowing in said helices causing like linear displacements ofsaid member on both sides of said point through the inherentmagnetostrictive qualities thereof and consequent vibration of thediaphragm.

2. In a sound reproducer, a plurality of'magnetostrictive members joinedat a central point by a flexible connection, coils around said membersconnected in a variable source of current, a diaphragm having its centerpoint connected to the junction point of the members, current changes inthe coils causing like linear displacements of said members to in turncause lateral movement of thejunction of the members and consequentvibration of the diaphragm.

3. In a sound reproducer, a diaphragm, a plurality of metallic membersjoined at a central point, the outer ends of said members being rigidlysecured, electromagnets encircling said members and connected in asource of alternating current, the variations in current in said coilscausing changes in length of the members and consequent lateral movementof the members at the central point, said diaphragm connected to thecentral point of the membersand vibrated thereby.

4. In a sound reproducer, a metallic member, a diaphragm connected to anintermediate point of the member, said member having a thin portionadjacent the connection to the diaphragm and adjacent its outer ends,said member rigidly secured at its outer ends and bent at an angle,

an electromagnet encircling said member and connected to a source ofvariable current, the changes in the current in said electromagnetcausing said member to elongate and contract and increase its angle tothereby vibrate the diaphragm.

5. In a sound reproducer, a diaphragm, a metallic member suspended in amagnetic field, said member secured at both ends and bent at an anglenear its central point, said diaphragm lic member, a link from the apexof the cone to an intermediate point of the member, both ends of themember bent at an angle away from the cone forming an angle the apex ofwhich is attached to the link, a coil surrounding each of the ends ofthe member and extending around an appreciable length thereof, saidcoils connected in a circuit including a variable source of current,said member secured so that variations in length cause maximum movementto occur at the apex of the member.

7. In a reproducer, a diaphragm, an operating unit for said diaphragmcomprising a completely closed metallic circuit, means for producing andvarying a magnetic flux in said metallic circuit, a magnetostrictiveelement in said circuit operable to elongate or contract responsive tochanges in the magnetic flux therethrough to vibrate the diaphragm.

8. In a sound reproducer, a metallicmember, having the samemagnetostrictive qualities throughout its length, rigidly secured atboth ends, a diaphragm secured to a point intermediate said ends, meansfor premagnetizing said rod, helices surrounding said rod and connectedin circuit with a variable source of alternating current, the variationsin current in said helices causing lateral displacement of said rod dueto the magnetostrictive qualities thereof, and consequent vibrations ofsaid diaphragm, said member arranged so that the lateral displacement ofsaid rod always occurs in the same plane.

9. In a sound reproducer, an operating member comprising a rod havinglike magnetostrictive qualities throughout its length, means forinitially magnetizing the rod to its most eflicient point of sensitivityon the magnetostrictive curve, an electromagnet associated with the rod,said rod rigidly secured at both ends and a diaphragm secured to a pointintermediate the ends, said electromagnet connected to a source ofalternating current and responsive to variations therein to causevariations in the length of the rod and consequent vibration of thediaphragm by lateral disp1acement of the intermediate point of the rod,said HARRY R. PARSHALL.

